1. Field of the Invention
The present invention relates to a fuel pump.
2. Description of the Related Art
A known fuel pump includes a casing and an impeller substantially in the form of a disk. The impeller has a circumferential array of vane grooves. The casing houses the impeller and has a pump passage, which is formed along the circumferential array, and through which fuel flows. The impeller can be rotated to suction fuel from the outside of the casing into the pump passage, pressurize the suctioned fuel, and discharge the pressurized fuel out of the casing (see JP-A-H9-512323, JP-A-2000-329085 corresponding to U.S. Pat. No. 6,336,788, and JP-A-2003-502580 corresponding to U.S. Pat. No. 6,474,937).
The fuel pump disclosed in each of JP-A-H9-512323 (corresponding to U.S. Pat. No. 5,785,490), JP-A-2000-329085, and JP-A-2003-502580 includes an impeller and a pump passage, which has a pressurizing passage and a discharge passage. The discharge passage extends from the downstream end of the pressurizing passage. The fuel pressurized by the rotation of the impeller flows through the pressurizing passage. The fuel pressurized in the pressurizing passage is discharged through the discharge passage in a direction away from the impeller toward a motor of the fuel pump.
In the fuel pump disclosed in each of JP-A-H9-512323 and JP-A-2000-329085, a passage width of the downstream end of the pressurizing passage becomes narrower toward the downstream side. A passage width of the discharge passage, which extends from the downstream end of the pressurizing passage, becomes wider toward the outlet of the discharge passage. The outlet is nearly equal or greater than the pressurizing passage in width. The radially inner wall of the discharge passage inclines inward from the inlet of the discharge passage to the outlet of the discharge passage.
In the fuel pump disclosed in JP-A-2003-502580, the discharge passage is narrower than the pressurizing passage. The inlet of this discharge passage opens at the bottom of the pressurizing passage.
Because the pressurizing passage extends along the circumferential array of vane grooves, centrifugal force acts on the fuel flowing through the pressurizing passage and the discharge passage. In the fuel pump disclosed in each of JP-A-H9-512323 and JP-A-2000-329085, a passage width of the downstream end of the pressurizing passage becomes narrower toward the downstream side, and the outlet of the discharge passage is nearly equal to or greater than the pressurizing passage in width. Because centrifugal force acts on the fuel flowing through the discharge passage, the fuel is out of contact with the radially inner wall of the discharge passage, so that a stagnant flow is prone to be made in the fuel passage.
If a stagnant flow is made near the radially inner wall of the discharge passage, a vortex is made in the flow. The fuel flowing into the discharge passage is directed to the radially outer wall of the discharge passage by the centrifugal force of the above made vortex. As a result, the fuel flowing near the radially outer wall is hindered from flowing toward the outlet of the discharge passage. Thus, even in a case, where the outlet is is made substantially equal to or greater than the pressurizing passage in width, the above hindering may decrease a sectional area of an effective part of a passage, though which the fuel to be discharged out of the casing member via the outlet flows disadvantageously. The above sectional area of the effective part is alternatively defined as an effective sectional area, in which the fuel effectively flows.
In the fuel pump disclosed in JP-A-2003-502580, the discharge passage, which is narrower than the pressurizing passage, extends from the bottom of the pressurizing passage. The sharp decrease in width at the junction of the two passages increases the energy loss in the fuel pump disadvantageously.